/*

* EAX Mode Encryption

* (C) 1999-2007 Jack Lloyd

* (C) 2016 Daniel Neus, Rohde & Schwarz Cybersecurity

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#include <botan/eax.h>

#include <botan/cmac.h>

#include <botan/ctr.h>

namespace Botan {

namespace {

/*

* EAX MAC-based PRF

*/

secure_vector<uint8_t> eax_prf(uint8_t tag, size_t block_size,

                           MessageAuthenticationCode& mac,

                           const uint8_t in[], size_t length)

   {

   for(size_t i = 0; i != block_size - 1; ++i)

      {

      mac.update(0);

      }

   mac.update(tag);

   mac.update(in, length);

   return mac.final();

   }

}

/*

* EAX_Mode Constructor

*/

EAX_Mode::EAX_Mode(BlockCipher* cipher, size_t tag_size) :

   m_tag_size(tag_size),

   m_cipher(cipher),

   m_ctr(new CTR_BE(m_cipher->clone())),

   m_cmac(new CMAC(m_cipher->clone()))

   {

   if(m_tag_size < 8 || m_tag_size > m_cmac->output_length())

      throw Invalid_Argument(name() + ": Bad tag size " + std::to_string(tag_size));

   }

void EAX_Mode::clear()

   {

   m_cipher->clear();

   m_ctr->clear();

   m_cmac->clear();

   reset();

   }

void EAX_Mode::reset()

   {

   m_ad_mac.clear();

   m_nonce_mac.clear();

   // Clear out any data added to the CMAC calculation

   try {

      m_cmac->final();

   }

   catch(Key_Not_Set&) {}

   }

std::string EAX_Mode::name() const

   {

   return (m_cipher->name() + "/EAX");

   }

size_t EAX_Mode::update_granularity() const

   {

   /*

   * For EAX this actually can be as low as 1 but that causes problems

   * for applications which use update_granularity as the buffer size.

   */

   return m_cipher->parallel_bytes();

   }

Key_Length_Specification EAX_Mode::key_spec() const

   {

   return m_cipher->key_spec();

   }

/*

* Set the EAX key

*/

void EAX_Mode::key_schedule(const uint8_t key[], size_t length)

   {

   /*

   * These could share the key schedule, which is one nice part of EAX,

   * but it's much easier to ignore that here...

   */

   m_ctr->set_key(key, length);

   m_cmac->set_key(key, length);

   }

/*

* Set the EAX associated data

*/

void EAX_Mode::set_associated_data(const uint8_t ad[], size_t length)

   {

   if(m_nonce_mac.empty() == false)

      throw Invalid_State("Cannot set AD for EAX while processing a message");

   m_ad_mac = eax_prf(1, block_size(), *m_cmac, ad, length);

   }

void EAX_Mode::start_msg(const uint8_t nonce[], size_t nonce_len)

   {

   if(!valid_nonce_length(nonce_len))

      throw Invalid_IV_Length(name(), nonce_len);

   m_nonce_mac = eax_prf(0, block_size(), *m_cmac, nonce, nonce_len);

   m_ctr->set_iv(m_nonce_mac.data(), m_nonce_mac.size());

   for(size_t i = 0; i != block_size() - 1; ++i)

      m_cmac->update(0);

   m_cmac->update(2);

   }

size_t EAX_Encryption::process(uint8_t buf[], size_t sz)

   {

   BOTAN_STATE_CHECK(m_nonce_mac.size() > 0);

   m_ctr->cipher(buf, buf, sz);

   m_cmac->update(buf, sz);

   return sz;

   }

void EAX_Encryption::finish(secure_vector<uint8_t>& buffer, size_t offset)

   {

   BOTAN_ASSERT_NOMSG(m_nonce_mac.empty() == false);

   update(buffer, offset);

   secure_vector<uint8_t> data_mac = m_cmac->final();

   xor_buf(data_mac, m_nonce_mac, data_mac.size());

   if(m_ad_mac.empty())

      {

      m_ad_mac = eax_prf(1, block_size(), *m_cmac, nullptr, 0);

      }

   xor_buf(data_mac, m_ad_mac, data_mac.size());

   buffer += std::make_pair(data_mac.data(), tag_size());

   }

size_t EAX_Decryption::process(uint8_t buf[], size_t sz)

   {

   BOTAN_STATE_CHECK(m_nonce_mac.size() > 0);

   m_cmac->update(buf, sz);

   m_ctr->cipher(buf, buf, sz);

   return sz;

   }

void EAX_Decryption::finish(secure_vector<uint8_t>& buffer, size_t offset)

   {

   BOTAN_ASSERT(buffer.size() >= offset, "Offset is sane");

   const size_t sz = buffer.size() - offset;

   uint8_t* buf = buffer.data() + offset;

   BOTAN_ASSERT(sz >= tag_size(), "Have the tag as part of final input");

   const size_t remaining = sz - tag_size();

   if(remaining)

      {

      m_cmac->update(buf, remaining);

      m_ctr->cipher(buf, buf, remaining);

      }

   const uint8_t* included_tag = &buf[remaining];

   secure_vector<uint8_t> mac = m_cmac->final();

   mac ^= m_nonce_mac;

   if(m_ad_mac.empty())

      {

      m_ad_mac = eax_prf(1, block_size(), *m_cmac, nullptr, 0);

      }

   mac ^= m_ad_mac;

   if(!constant_time_compare(mac.data(), included_tag, tag_size()))

      throw Invalid_Authentication_Tag("EAX tag check failed");

   buffer.resize(offset + remaining);

   m_nonce_mac.clear();

   }

}